Actually, Borax has been used for years as a water softener, and works very similar to Calgon.
There are two types of packaged water conditioners: non-precipitating and precipitating.
Non-precipitating water conditioner ties up hardness minerals in the water and holds them in solution (sequestering). No visible particles are formed, water remains clear, they usually contains phosphates, they make the water feels slippery. Examples are Calgon (a mixture of non-precipitating (Trisodium Citrate Dihydrate) and precipitating chemicals (Sodium Carbonate) and Sodium Sulfate), White Rain, Blue Raindrops, Spring Rain, etc.
Precipitating water softener combines with hardness minerals to form a visible, insoluble precipitate that floats on top of water and makes the water cloudy and is highly alkaline. Examples are Arm and Hammer Washing Soda (Sodium Carbonate), Raindrops, Blue Dew, Borax, Climalene, Melo, White King Water Softener, etc.
Of course, the most common type of water softening is using zeolite in an ion exchange column, i.e., the common salt regenerated water softener. We have one in our RV, but not many do due to space requirement, and regeneration requirements.
Rick & Debbie; Brandy & Schnoodle Dexter & Fritz R.I.P. the Doxie "Kids"
2015 Jayco Pinnacle 36RSQS 5'er
2013 Chevy Silverado 3500HD LTZ, 6.6L Diesel Dually; B&W Goose Neck and Companion 5'er hitch